diff --git a/relaykit/dto/openai_response.go b/relaykit/dto/openai_response.go
index 945d0a869904..7a0e8ded9d95 100644
--- a/relaykit/dto/openai_response.go
+++ b/relaykit/dto/openai_response.go
@@ -123,7 +123,7 @@ type ToolCallResponse struct {
 	// Index is not nil only in chat completion chunk object
 	Index    *int             `json:"index,omitempty"`
 	ID       string           `json:"id,omitempty"`
-	Type     any              `json:"type"`
+	Type     any              `json:"type,omitempty"`
 	Function FunctionResponse `json:"function"`
 }
 
diff --git a/relaykit/relayconvert/internal/oai_responses/to_oai_chat_resp_test.go b/relaykit/relayconvert/internal/oai_responses/to_oai_chat_resp_test.go
index 49efa07d163e..eaec34d55ecc 100644
--- a/relaykit/relayconvert/internal/oai_responses/to_oai_chat_resp_test.go
+++ b/relaykit/relayconvert/internal/oai_responses/to_oai_chat_resp_test.go
@@ -1,6 +1,7 @@
 package oairesponses
 
 import (
+	"encoding/json"
 	"testing"
 
 	"github.com/QuantumNous/new-api/relaykit/dto"
@@ -246,6 +247,135 @@ func TestResponsesStreamEventToChatChunksCustomToolAndReasoning(t *testing.T) {
 	assert.Equal(t, "content_filter", *chunks[4].Choices[0].FinishReason)
 }
 
+func TestResponsesStreamEventToChatChunksEmitsToolMetadataOnlyOnce(t *testing.T) {
+	state := newTestResponsesStreamState()
+	outputIndex := 0
+
+	itemChunks := mustStreamChunks(t, state, &dto.ResponsesStreamResponse{
+		Type:        responsesEventOutputItemAdded,
+		OutputIndex: &outputIndex,
+		Item: &dto.ResponsesOutput{
+			Type:   responsesOutputTypeFunctionCall,
+			ID:     "fc_1",
+			CallId: "call_1",
+			Name:   "show_widget",
+		},
+	})
+	firstArgsChunks := mustStreamChunks(t, state, &dto.ResponsesStreamResponse{
+		Type:        responsesEventFunctionArgsDelta,
+		OutputIndex: &outputIndex,
+		Delta:       `{"widget_code":"<svg>`,
+	})
+	secondArgsChunks := mustStreamChunks(t, state, &dto.ResponsesStreamResponse{
+		Type:        responsesEventFunctionArgsDelta,
+		OutputIndex: &outputIndex,
+		Delta:       `</svg>"}`,
+	})
+
+	require.Len(t, itemChunks, 2)
+	require.Len(t, firstArgsChunks, 1)
+	require.Len(t, secondArgsChunks, 1)
+
+	first := itemChunks[1].Choices[0].Delta.ToolCalls[0]
+	assert.Equal(t, "call_1", first.ID)
+	assert.Equal(t, "function", first.Type)
+	assert.Equal(t, "show_widget", first.Function.Name)
+
+	for i, chunks := range [][]dto.ChatCompletionsStreamResponse{firstArgsChunks, secondArgsChunks} {
+		continuation := chunks[0].Choices[0].Delta.ToolCalls[0]
+		require.NotNil(t, continuation.Index)
+		assert.Equal(t, 0, *continuation.Index)
+		assert.Equal(t, []string{`{"widget_code":"<svg>`, `</svg>"}`}[i], continuation.Function.Arguments)
+		assert.Empty(t, continuation.ID)
+		assert.Nil(t, continuation.Type)
+		assert.Empty(t, continuation.Function.Name)
+
+		encoded, err := json.Marshal(continuation)
+		require.NoError(t, err)
+		assert.NotContains(t, string(encoded), `"id"`)
+		assert.NotContains(t, string(encoded), `"type"`)
+		assert.NotContains(t, string(encoded), `"name"`)
+	}
+}
+
+func TestResponsesStreamEventToChatChunksEmitsMetadataForEachParallelTool(t *testing.T) {
+	state := newTestResponsesStreamState()
+	firstOutputIndex := 0
+	secondOutputIndex := 1
+
+	firstChunks := mustStreamChunks(t, state, &dto.ResponsesStreamResponse{
+		Type:        responsesEventOutputItemAdded,
+		OutputIndex: &firstOutputIndex,
+		Item: &dto.ResponsesOutput{
+			Type:   responsesOutputTypeFunctionCall,
+			CallId: "call_1",
+			Name:   "first_tool",
+		},
+	})
+	secondChunks := mustStreamChunks(t, state, &dto.ResponsesStreamResponse{
+		Type:        responsesEventOutputItemAdded,
+		OutputIndex: &secondOutputIndex,
+		Item: &dto.ResponsesOutput{
+			Type:   responsesOutputTypeFunctionCall,
+			CallId: "call_2",
+			Name:   "second_tool",
+		},
+	})
+	firstArgsChunks := mustStreamChunks(t, state, &dto.ResponsesStreamResponse{
+		Type:        responsesEventFunctionArgsDelta,
+		OutputIndex: &firstOutputIndex,
+		Delta:       `{"first":`,
+	})
+	secondArgsChunks := mustStreamChunks(t, state, &dto.ResponsesStreamResponse{
+		Type:        responsesEventFunctionArgsDelta,
+		OutputIndex: &secondOutputIndex,
+		Delta:       `{"second":`,
+	})
+	firstArgsEndChunks := mustStreamChunks(t, state, &dto.ResponsesStreamResponse{
+		Type:        responsesEventFunctionArgsDelta,
+		OutputIndex: &firstOutputIndex,
+		Delta:       `"one"}`,
+	})
+	secondArgsEndChunks := mustStreamChunks(t, state, &dto.ResponsesStreamResponse{
+		Type:        responsesEventFunctionArgsDelta,
+		OutputIndex: &secondOutputIndex,
+		Delta:       `"two"}`,
+	})
+
+	require.Len(t, firstChunks, 2)
+	require.Len(t, secondChunks, 1)
+
+	first := firstChunks[1].Choices[0].Delta.ToolCalls[0]
+	second := secondChunks[0].Choices[0].Delta.ToolCalls[0]
+	assert.Equal(t, "call_1", first.ID)
+	assert.Equal(t, "function", first.Type)
+	assert.Equal(t, 0, *first.Index)
+	assert.Equal(t, "call_2", second.ID)
+	assert.Equal(t, "function", second.Type)
+	assert.Equal(t, 1, *second.Index)
+
+	continuations := []struct {
+		chunks    []dto.ChatCompletionsStreamResponse
+		index     int
+		arguments string
+	}{
+		{firstArgsChunks, 0, `{"first":`},
+		{secondArgsChunks, 1, `{"second":`},
+		{firstArgsEndChunks, 0, `"one"}`},
+		{secondArgsEndChunks, 1, `"two"}`},
+	}
+	for _, tt := range continuations {
+		require.Len(t, tt.chunks, 1)
+		continuation := tt.chunks[0].Choices[0].Delta.ToolCalls[0]
+		require.NotNil(t, continuation.Index)
+		assert.Equal(t, tt.index, *continuation.Index)
+		assert.Equal(t, tt.arguments, continuation.Function.Arguments)
+		assert.Empty(t, continuation.ID)
+		assert.Nil(t, continuation.Type)
+		assert.Empty(t, continuation.Function.Name)
+	}
+}
+
 func TestResponsesStreamEventToChatChunksUsesTerminalDoneOutput(t *testing.T) {
 	state := newTestResponsesStreamState()
 	chunks := mustStreamChunks(t, state, &dto.ResponsesStreamResponse{
diff --git a/relaykit/relayconvert/internal/oai_responses/to_oai_chat_stream_resp.go b/relaykit/relayconvert/internal/oai_responses/to_oai_chat_stream_resp.go
index 6026e3899eeb..769ec4c27f57 100644
--- a/relaykit/relayconvert/internal/oai_responses/to_oai_chat_stream_resp.go
+++ b/relaykit/relayconvert/internal/oai_responses/to_oai_chat_stream_resp.go
@@ -397,25 +397,25 @@ func (s *ResponsesToChatStreamState) toolDelta(tool *responsesStreamTool, explic
 	}
 
 	chunks := s.ensureStart()
-	callID := strings.TrimSpace(tool.CallID)
-	if callID == "" {
-		callID = tool.Key
-	}
 	responseTool := dto.ToolCallResponse{
-		ID:   callID,
-		Type: "function",
 		Function: dto.FunctionResponse{
 			Arguments: argsDelta,
 		},
 	}
 	responseTool.SetIndex(tool.Index)
+	if !tool.Sent {
+		callID := strings.TrimSpace(tool.CallID)
+		if callID == "" {
+			callID = tool.Key
+		}
+		responseTool.ID = callID
+		responseTool.Type = "function"
+		tool.Sent = true
+	}
 	if !tool.NameSent && tool.Name != "" {
 		responseTool.Function.Name = tool.Name
 		tool.NameSent = true
 	}
-	if !tool.Sent {
-		tool.Sent = true
-	}
 	if argsDelta != "" {
 		tool.ArgsSentAt += len(argsDelta)
 		s.usageText.WriteString(argsDelta)